An important use of computers is the transfer of information over a network. Currently, the largest computer network in existence is the Internet, which is a worldwide interconnection of millions of computers, from low end personal computers to high-end mainframes.
The Internet grew out of work funded in the 1960s by the U.S. Defense Department's Advanced Research Projects Agency. For a long time, Internet was used by researchers in universities and national laboratories to share information. As the existence of the Internet became more widely known, many users outside of the academic/research community (e.g., employees of large corporations) started to use Internet to carry electronic mails. In 1989, a wide-area information system know as the World Wide Web ("the Web") was originated at CERN, which is a European collective of high-energy physics researchers. The Web is a wide-area hypermedia information retrieval system aimed to give universal access to a large universe of documents. At that time, the Web was known to and used by the academic/research community only. There was no easily available tool which allows a technically untrained person to access the Web. The most exciting development in Internet is the release of a Web "browser" called Mosaic in 1993. It has a simple but powerful graphic interface. The browser allows a user to retrieve web documents and navigate the Web using simple commands and popular tools such as point-and-click. Because the user does not have to be technically trained and the browser is pleasant to use, it has the potential of opening up the Internet to the masses.
A document designed to be accessed and read over the web is called a web page. Each web page must have an address in a recognized format--the URL, or Uniform Resource Locator--that enables computers all over the world to access it. Each web page has an unique URL. A web page typically contains both text and images. Because image files are large, even when compressed, it could take a long time to retrieve a web page, especially when a voice-quality phone line is used to connect to the Internet. Consequently, it is important to design a browser which is able to reduce the amount of time to display a web page.
Some browsers display a web page on a computer screen only when all the data (i.e., text and images) is received. As a result, the computer screen becomes blank for an unbearable period of time (e.g., many minutes) after a request for the web page is made. Other browsers display the text before the images are received. These browsers may use icons at appropriate places on a web page to indicate that images would appear at these places later. When the images are received, the page needs to be reformatted because the sizes of the icons are different from the sizes of the images. The reformatting process produces a sudden and annoying change on the computer screen.
In order to encourage more users to use the Web, it is desirable to reduce the time a web page appears on a computer screen and to display web pages in a more appealing fashion.